Create a saved search that finds the books you want. Go to preferences -> behavior -> "restriction to apply when the current library is opened" and select that saved search. From then on, when you open that library you will see only those books. You see all books by changing the box near the top left that will be showing the search name to contain nothing.

You switch libraries by clicking the down arrow on the library toolbar icon (the picture of some books) and selecting "Switch/create library". Navigate to the other library, select the radio button "Use the previously existing library at the new location", and press OK.

[EDIT: I should learn to refresh the thread before I answer to avoid redundant posts if someone else has already answered]